Dynorphin, a very powerful endogenous opioid ligand, is a 17-amino acid brain natural peptide that plays a major role in pain control and in the regulation of immune response. It also promotes emotional balance, enhances mental activity and reduces feelings that lead to compulsive behavior. This peptide contains a pleasure producing substance known as leu-enkephalin at the NH2 terminus of the sequence. Dynorphins also have a high affinity for x-receptors that mediate many of the unpleasant dysphoric side effects of opioids. Dynorphin A peptides provide analgesia and also prevent or reverse opiate withdrawal signs and symptoms in morphine-dependent animals and possibly also in humans.